Rotary valves of this kind are usually used for conveying or metering bulk material. A cellular wheel is rotatably supported in the cavity and includes a plurality of cells which are charged with bulk material from above through the supply opening of the housing. The supply opening or shaft may be in communication with a vessel, such as a storage bin. When the cellular wheel rotates, the bulk material is introduced through the discharge opening, for example, into a pneumatic conveyor conduit where it is conveyed by a gas under pressure to a desired location.
Since ordinarily the bin is under a smaller gas pressure than the pneumatic conveyor conduit, it is usual to make the cellular tightly sealed or fitting in the housing's cavity. However, when defining the dimensions it has to be taken into account that the cellular wheel may be radially shifted by a small amount due to the difference in pressure between the discharge opening and the supply opening.
Furthermore, when the gas under pressure streams from the conveying conduit and the discharged cells upwards, this results in local cooling and, thus, a distortion which reduces the inner dimensions of the cavity. Likewise, when hot bulk material is conveyed, the cavity may experience a certain expansion, thus enlarging its inner dimensions. In all these cases, the distance between the outer circumference of the cellular wheel and the inner dimensions of the cavity will no longer be maintained in the desired range or at a certain nominal value desired.
A rotary valve of the type described at the outset is known from EP 0 732 280 A1 the disclosure of which is hereby incorparated by reference in its entirety. In this document, a rotary valve is described having a conical cellular wheel in a fitting cavity so that the distance or gap between the outer radial dimensions or periphery of the cellular wheel and the inner radial dimensions of the cavity may be adjusted by shifting the cellular wheel in axial direction in the cavity. There is a shifting drive for the cellular wheel and a control unit which maintains this gap automatically at the smallest possible value for enabling, nevertheless, rotation of the wheel. The shifting drive is periodically operated by the control unit for re-reducing the gap when it has become larger due to wear. To determine this fact, the drive torque necessary to rotate the cellular wheel is measured. If the drive torque reaches a pre-adjusted maximum value due to increasing friction when shifting the conical cellular wheel in the hollow conical cavity, the cellular wheel is shifted back by a well-defined stroke in axial direction to enable proper rotation so that the value of the gap will finally be reduced to a desired nominal value of 0.1 mm, for example.
This procedure involves, however, various disadvantages. First, this procedure can only be applied to rotary valves having a conical cellular wheel, because axially shifting a cylindrical wheel in a cylindrical cavity would not alter the gap between them. Second, the procedure means that the cellular wheel and the inner wall of the cavity may contact each other, which may destroy their surfaces when they are made of sensitive materials, for example, if they are both made of special steel.
Document DE 298 19 747 U1 the disclosure of which is hereby incorparated by reference in its entirety discloses locally influencing the radial dimensions of a cavity by locally heating the housing. By heating the housing, reduction of the inner diameter of the cavity shall be prevented which is due to the flash of conveying gas when leakage gas from the rotary valves escapes, thus provoking cooling both of the gas and the housing. The actual gap width or distance between the outer radial dimensions of the cellular wheel and the inner radial dimensions of the cavity is not determined neither indirectly nor directly.
Furthermore, it is known from German Publication No. DE-A-2,339,135, the disclosure if which is hereby incorparated by reference in its entirety, to change the diameter of a cellular wheel by inflating special hose-like elements which are arranged radially outside on the partitions When the rotary valves is stopped, the outer radial dimensions of the cellular wheel are enlarged so that it sealingly engages the inner wall of the cavity. In this way, the use of any additional sliding valve as a shutter can be avoided. Before operating the rotary valve, the hose-like seals are biased by pressurized air so that they may disengage the inner wall of the cavity due to their special shape.
Another rotary valve of the type described at the outset is disclosed in Austrian Patent (AT) No. 279 482 the disclosure of which is hereby incorparate by reference in its entirety. According to this document, the cavity is provided with a deformable, hose-like inner lining of rubber or an elastomer which is pressed in radial direction against the circumference of the cellular wheel to engage tightly the partitions by supplying a pressure medium into a gap between the housing and the inner lining.
However, it is not acceptable or even permissible that the partitions of the cellular wheel and the stationary walls of the housing contact each other if they are made of metal.